If some public-health advocates have their way, sodas could become the cigarettes of food. Doctors already dislike the sugary drinks for their teeth-dissolving properties and for the role they may play in childhood obesity. There’s a constant struggle to get soda vending machines out of public schools, with administrators often forced to choose between losing sponsorship money from big soda companies and dealing with overcaffeinated, less healthy kids. Given the sheer size of the American soda industry — 9.4 billion cases of soft drinks were sold in the U.S. in 2009 — it’s not a war that will end anytime soon. Especially if a certain C word starts getting thrown around.

That’s what the Center for Science in the Public Interest (CSPI) is doing. The consumer watchdog group yesterday wrote a letter to the U.S. Food and Drug Administration (FDA) calling on officials to ban the use of caramel coloring — the additive that makes cola brown — in soft drinks on the grounds that the chemicals are a possible cancer risk. In the letter to FDA administrator Margaret Hamburg, CSPI executive director Michael Jacobson argued that recent lab analyses show that levels of 4-methylimidazole (4-MI) — which, along with 2-methylimidazole, is formed when sugar is mixed with ammonia and sulfates to create caramel coloring — in 12-oz. servings of soda exceed by nearly five times the 29-microgram limit recommended by the state of California.

The group estimated that the average amount of 4-MI in soda translates in the population to a lifetime cancer risk of 5 out of 100,000 people. “Coke and Pepsi, with the acquiesence of the FDA, are needlessly exposing millions of Americans to a chemical that causes cancer,” Jacobson said in a statement.

The FDA doesn’t seem to think so. In a statement released on Tuesday, March 6, FDA spokesman Doug Karas said that according to national standards, soda contains far too little 4-MI to pose much of a cancer risk:

A consumer would have to consume well over a thousand cans of soda a day to reach the doses administered in the studies that have shown links to cancer in rodents.

The FDA limit for 4-MI in caramel coloring is 250 parts per million (ppm), and the caramel is diluted when it’s put into soda. Reuters calculated that the highest levels of 4-MI found by the CSPI were about 0.4 ppm, which means you’d be hard-pressed to expose yourself to enough 4-MI to face much cancer risk.

Unsurprisingly, the American Beverage Association, a trade group that includes soda manufacturers, also dismissed the cancer risk from caramel coloring:

The science simply does not show that [4-MI] in foods or beverages is a threat to human health. In fact, findings of regulatory agencies worldwide, including the U.S. Food and Drug Administration, European Food Safety Authority and Health Canada, consider caramel coloring safe for use in foods and beverages.

And the CSPI admits that soda drinkers should be much more worried about the high-fructose corn syrup and other sugars loaded into sodas, which contribute to obesity, diabetes and other health problems. (A 2009 study by UCLA directly connected soda consumption to obesity.) Still, it’s interesting that one sodamaker, Pepsi, told the CSPI it would be switching to a caramel coloring that uses much less 4-MI, first in California and then nationwide. And as Jacobson notes, the caramel coloring in soda is purely cosmetic, meaning it could be removed with no changes in soda’s taste. “If companies can make brown food coloring that is carcinogen-free, the industry should do that,” Jacobson says. “Otherwise the FDA needs to protect consumers from this risk by banning the coloring.”

I don’t see the FDA going down that road, given the sheer muscle of the soft-drink industry — and the fact that the evidence doesn’t show 4-MI in soda to be a clear-cut cancer risk. The fate of Crystal Pepsi, the short-lived clear soda from the 1990s, suggests that soda companies wouldn’t be eager to change something as integral as color to the consumer experience of cola drinking. But caramel coloring or not, no one would argue that drinking soda in the Super Big Gulp quantities that many Americans do is anything but bad for your health, and the fact that per capita soda consumption has fallen 16% since 1998 indicates that many people are getting that message. The soda industry might dismiss the CSPI’s cancer crusade, but that doesn’t mean companies like Coke and Pepsi shouldn’t be worried.